The mitral valve lies between the left atrium and the left ventricle of the heart. Various diseases can affect the function of the mitral valve, including degenerative mitral valve disease and mitral valve prolapse. These diseases can cause mitral stenosis, in which the valve fails to open fully and thereby obstructs blood flow, and/or mitral insufficiency, in which the mitral valve is incompetent and blood flows passively in the wrong direction.
Many patients with heart disease, such as problems with the mitral valve, are intolerant of the trauma associated with open-heart surgery. Age or advanced illness may have impaired the patient's ability to recover from the injury of an open-heart procedure. Additionally, the high costs are associated with open-heart surgery and extra-corporeal perfusion can make such procedures prohibitive.
Patients in need of cardiac valve repair or cardiac valve replacement can be served by minimally invasive surgical techniques. In many minimally invasive procedures, small devices are manipulated within the patient's body under visualization from a live imaging source like ultrasound, fluoroscopy, or endoscopy. Minimally invasive cardiac procedures are inherently less traumatic than open procedures and may be performed without extra-corporeal perfusion, which carries a significant risk of procedural complications.
Minimally invasive aortic valve replacement devices, such as the Medtronic Corevalve or the Edwards Sapien, deliver aortic valve prostheses through small tubes which may be positioned within the heart through the aorta via the femoral artery or through the apex of the heart. However, current cardiac valve prostheses are not designed to function effectively within the mitral valve. Further, current cardiac valve prostheses delivered via a minimally invasive device are often difficult to place correctly within the native valve, difficult to match in size to the native valve, and difficult to retrieve and replace if initially placed incorrectly. Furthermore, the mitral valve differs from the aortic valve in that the shape and anatomy immediately surrounding the valve varies greatly from one side of the valve to the other. One access route for delivering replacement mitral valves requires a transseptal approach. Delivering a replacement valve transseptally imparts limitations on the size of the delivery device and the delivery profile of the replacement valve within the delivery device, and imparts certain flexibility requirements for the replacement valve itself as it is delivered transseptally to the location of the native mitral valve. In some embodiments a sheath passing through a septum should be at most about 24F-28F.
Many current minimally invasive valve devices are made from super-elastic Nickel-Titanium alloys. These super-elastic alloys allow high material strains, usually 6%-8%, without permanent deformation. Therefore, the alloys allow the valve devices to be packed into a small 6-10 mm diameter tube for delivery while expanding to around 50 mm within the heart. Current manufacturing methods typically involve cutting the valve prosthesis, at least the expandable anchor portion thereof, from a single tubular element that has a uniform thickness along its length. In these cases, the cut expandable anchor may have the same thickness along its length, and thus may not have varying stiffness along the length of the device. The inability to create an expandable anchor with varying thickness throughout can limit the functionality of different regions of the expandable anchor. Certain regions of the expandable anchor may be limited in what they can be configured to perform by creating the valve from a single tubular element. This can be undesirable if there is a need to create certain functionality in different regions of the expandable anchor that result from the regions have different thicknesses. Similarly, traditional expandable anchors made from a single tubular element do not have overlapping components (radially), wherein overlapping components may help impart additional flexibility to portions of the expandable anchor, and/or allow the expandable anchor to be collapsed to have a smaller delivery profile. Furthermore, in a single-piece construction, strains are limited to the elastic strain limit of the material, which may be too low for some applications.
These and other deficiencies in existing approaches are described herein.